What should I do?
Go to the police.
You were physically assaulted and suffered permanent damage. This is not something to be taken lightly and is on a completely different level than a few bruises from a friendly fight.
a) you were attacked against your will. This makes it legally an assault or a comparable crime. You didn't add a country tag, but in many countries not reporting a crime is a crime in itself.
b) you lost a tooth. Teeth don't grow back. You will have this damage for the rest of your life, and even if you get an artificial replacement tooth, the fact that permanent damage was done can put this - again depending on jurisdiction - into the area of serious criminal assault, essentially legally the same as if they had hacked off a finger.
c) you are suffering from psychological stress afterwards. This is another harm done to you and in fact I recommend you see a psychologist to prevent PTSD from manifesting, which would seriously impact you for life.
Seriously, go to the police. Name place, time and - most importantly - witnesses. People who might say that nothing happened if questioned by you or HR because the guy is their boss, too, may be much more open talking to a police officer and can be taken under oath to speak the truth by a judge.